Keep in mind that all these results are temporary and subject to more calibration.

Single Species Insight

So we can run the model as a single species “snapper” complex. What we get, basically, is that no real improvement is possible for biomass without blocking also the small boats (5-15GT).

Look at the landings for each fleet (small, medium, large) when we block only large longliners from going out (darker color are simulations with more stringent effort control; darkest is 50 days out at max):

compared to when we block everybody:

Moving multispecies

Now, it may be hoped that for at least some species the result is different. From the data we have it looks like the second major product of the fishery (Pristipomoides Multidens) is mostly caught by medium and large dropliners (about 60-70%).
Is it then possible to at least protect this species by focusing on the largest boats?

The answer is, not really. What happens is that small and medium boats pick up the slack and within a few years are landing at the same level as before. Two adaptations are taking place:

Blocking medium boats too

What about blocking both medium and large boats? That actually gets us somewhere. Not really back to MSY but at least you can see a strong effect for policy. Except for malabaricus, the big 712 target which is still mostly driven by small boats.

Notice that the adaptation effects (higher CPUE for medium boats and target switching for small boats) are still there, just not enough to block some biological progress.

Blocking all boats

Clearly small boats need to be included in the season closure if we want to get anything done. Notice however that even with very short 50 day season the malabaricus stock will not replenish to MSY (50% of \(K\) under logistic assumptions). This makes sense because it starts at a very low level of biomass.

Now, more importantly we can look at what it means in terms of money for small boats. This is what the next plot shows. Basically each “row” is a separate timeline where in 2018 we impose season quota. At the top (where \(y=200\)) is a fishery where no season was imposed (200 days is the maximum number of days they go out anyway) and at the bottom is a fishery where only 50 days of fishing are allowed by 2018. The color represents the ratio between profits that year and profits in 2017. White means about the same profits, red means lower profits, blue means higher profits. 2017 there is no season closure so everything is white. Then for the first few years the fisheries that are more heavily regulated have lower profits; as time goes by fisheries that are lightly regulated see their profits get redder and redder while fisheries that are highly regulated eventually (in about 8 years) see their profits rise back to original levels and then higher still.

Cheating